Make inner_wall_speed multi-variant

src/libslic3r/GCode.hpp

@@ -383,6 +383,7 @@ private:
 
     //BBS
     void check_placeholder_parser_failed();
+    size_t cur_extruder_index() const;
     size_t get_extruder_id(unsigned int filament_id) const;
 
     void            set_last_pos(const Point &pos) { m_last_pos = Point3(pos, 0); m_last_pos_defined = true; }